Keep a stiff upper lip
Remain resolute and unemotional in the face of adversity, or even tragedy.
This is such a clichéd expression that it is difficult to imagine doing anything else with a stiff upper lip apart from keeping it. If you try to hold your upper lip stiff your facial expression will appear aloof and unsmiling, betraying little of any feeling you might be experiencing. That demeanour is the source of 'keep a stiff upper lip'. The phrase is similar to 'bite the bullet', 'keep your chin up', and (to the amusement of many Americans) 'keep you pecker up'. It has become symbolic of the British, and particularly of the products of the English public school system during the age of the British Empire. In those schools the 'play up and play the game' ethos was inculcated into the boys who went on to rule the Empire. That 'do your duty and show no emotion' attitude was expressed in Alfred, Lord Tennyson's The Charge of the Light Brigade:
Theirs not to make reply,
Theirs not to reason why,
Theirs but to do and die:
Into the valley of Death
Rode the six hundred.
In more recent years the stiff upper lip has gone out of favour in the UK and British heroes have been able to show more emotion. Footballers now cry when they lose and soldiers cry at comrades' funerals, both of which would have been unthinkable before WWII.
So, where did the 'stiff upper lip' originate? In 1963, P. G. Wodehouse published a novel called Stiff Upper Lip, Jeeves, and you can't get much more English than that.
Strange then that a phrase so strongly associated with the UK should have originated in America. The first printed reference to it that I know of is in the Massachusetts Spy, June 1815:
"I kept a stiff upper lip, and bought [a] license to sell my goods."
That citation doesn't explicitly refer to keeping one's emotions in check, but a slightly later one, from the Ohio newspaper The Huron Reflector, 1830, makes the meaning unambiguous:
"I acknowledge I felt somehow queer about the bows; but I kept a stiff upper lip, and when my turn came, and the Commodore of the Police axed [sic] me how I come to be in such company... I felt a little better."
The expression can be found in several US references from the early 19th century and was commonplace there by 1844, which is the date of the earliest example that I can find from a British source.
'Keep a stiff upper lip' is one of the many phrases in English that are used to give advice. Other 'keep' expressions include: